It is generally known in powertrain controls to adjust ignition timing and engine inlet air rate to improve powertrain control stability. Compensation is provided for mechanical load disturbances by sensing or predicting the disturbance and by commanding compensating engine output torque variations. Powertrain mechanical load disturbances include transmission gear changes and application and removal of accessory loads. The powertrain is very sensitive to such disturbances during engine idle operating conditions at which the disturbances may cause a perceptible engine speed or torque perturbation. Engine temperature, speed, and load may be used to quantify the appropriate level of torque compensation for a sensed or predicted disturbance. The compensation may take the form of a variation in ignition timing to modulate engine output torque. A timing offset may be referenced or calculated and the ignition timing of individual engine cylinders adjusted in accord therewith to mitigate the disturbance.
The application of the offset provides a step change in ignition timing resulting in a sudden change in engine output torque. Such a sudden change may not be properly timed to adequately compensate certain disturbances, such as disturbances that are not characterized by a sudden or immediate engine output torque change.
Furthermore, conventional compensation for powertrain load disturbances associated with a transmission gear change do not adequately account for transmission dynamics and the effect of transmission temperature on such dynamics. Transmission responsiveness varies significantly with temperature, yet conventional timing offsets are commonly calibrated at a given transmission temperature and then applied over the broad range of transmission operating temperatures. Only when the transmission is at the calibration temperature will such conventional compensation properly compensate the disturbance.
The conventional compensation may generate or reference the timing offset as a function of engine speed during an operating mode in which engine speed is not stable. For example, engine speed may be varying under the influence of an independent control process when the speed dependent timing offset is generated. A duplication in control compensation may result which can reduce control effectiveness and stability.
Accordingly, what is needed is a powertrain control which compensates for engine speed in a stable manner, closely modelling the timing and magnitude of the disturbance.